2.4 capacitance

Question 1

how does relative permittivity affect capacitance

Answer 1

greater permittivity = greater capacitance

Question 2

What does the area under the graph of a charge against pd represent

Answer 2

Energy stored by the capacitor

Question 3

How does a capacitor charge up

Answer 3

• When the switch is closed, electrons flow onto one plate of the capacitor and away from the other, causing charge to build up on the plates.
• initially, the pd across the capacitor is zero, so current in the circuit is max
• as charge accumulated, pd across capacitor increases, decreasing pd across resistor
• current decrease exponentially
• capacitor becomes fully charged and current falls to zero
• pd across capacitor = emf of supply

Question 4

define capacitance

Answer 4

charge stored per unit charge

Question 5

uses of capacitors

Answer 5

• timing circuits
• smoothing p.d.
• filtering
• tuning
• storing energy

Question 6

with capacitors in series what is always the same

Answer 6

charge

Question 7

with capacitors in parallel what is always the same

Answer 7

potential difference

Question 8

how to work out capacitance in series

Answer 8

(c1^1 + c2^-1…)^-1

Question 9

how to work out capacitance in parallel

Answer 9

c1 + c2…